Past climates changed abruptly, suggesting that abrupt changes in the future will also occur, according to a Penn State geoscientist.

“When we look at records of the past, climate often changed abruptly rather than smoothly,” says Dr. Richard B. Alley, the Evan Pugh professor of geosciences at Penn State. “This is true wherever and whenever you look.”

Alley, who is currently chairing the National Academy of Science Committee on Abrupt Climate Change: Science and Public Policy, told attendees Thursday (Dec. 13) at the fall meeting of the American Geophysical Association in San Francisco, that while studies of ice cores, sediments and other relics of the past indicate these abrupt changes, the models currently used by those predicting the future of climate change do not do a good job of simulating abrupt changes in the past.

(Editor's Note: Dr. Alley's statement carries more of a warning tone than did the committee report, covered by UniSci in its lead story yesterday.)

“If we look at what we know about climate, there is much we don’t understand,” says Alley. “However, we do know that abrupt change occurred in the past.”

The abrupt changes are especially notable in temperature near the north and south poles and in precipitation away from the poles. In the near term, nature sometimes changes smoothly, sometimes remains the same and sometimes changes all at once. In the long term, abrupt change appears to be the norm. Current models all tend to change smoothly and do not capture abruptness.

“It is possible that climate change in the future will include abruptness, even though the current models do not show this,” says Alley.

The Penn State geoscientist suggests that climate change includes a process of approaching and crossing a series of thresholds. Climate forcing factors are like a tower of blocks. Building the tower, blocks can be added, and the tower remains stable, but eventually the block height crosses the threshold of stability and the tower abruptly topples. With climate, the thresholds in the past have sometimes been reached in as few as 10 years.

“It will be a long time, if at all, before we are really good at predicting climate change and it may not be easy,” Alley says. “Any reality may be very different from the predictions and we need to anticipate changes and surprises. We need to build uncertainty into our models of dealing with climate change.” - By A'ndrea Elyse Messer